The invention concerns an apparatus for transferring heat from a first fluid to a second fluid—which is separated from the first fluid—having a stack-like or saucer-like structure comprising at least two plies, in particular plates.
Until now, heat exchangers, for example, comprising a first passage through which a high pressure-side refrigerant flows, and a second passage—which is separated from the first passage—through which a low pressure-side refrigerant flows, are provided in a CO2 vehicle air conditioner.
In order to increase the output and efficiency of the CO2 process, an “inner” or “internal” heat exchanger is provided. Refrigerant (CO2) flows through the internal heat exchanger in cocurrent or counterflow. According to this, the fluids flow through the heat exchanger once on the way from the vapor cooling apparatus to the evaporator and, the second time, they flow between the evaporator and the compressor. The main function of the internal heat exchanger in this context is to further cool the refrigerant before expansion. The heat is transferred from the high-pressure side [word missing] the vapor cooling apparatus to the low-pressure side after the evaporator (before it enters the compressor). The refrigerant—which is still partially liquified—evaporates completely before it reaches the compressor.
Potential applications of heat exchangers of this type include vehicle air conditioners, heat pumps, portable low-output air conditioners, air dehumidifiers, driers, fuel cell systems, and the like.
Heat exchangers that are produced relatively compact in size in order to reduce mass and volume have already been made known. In order to transfer large quantities of heat using a small design, “micro heat exchangers” are provided, for example. They comprise, in particular, structured plates stacked on top of each other and joined together via soldering, screw connection, or the like. This also seals off passages in the heat exchanger provided in appropriate fashion. The fluids that come in thermal contact with each other in the heat exchanger are conducted between the plates via the passages.
In the micro heat exchanger, the fluids are conducted into the individual plies via inlet openings or exit openings, so that a heat-absorbing and a heat-dissipating fluid flows through various plies in alternating fashion. The distribution or bringing together of the fluids into or out of the individual passages takes place in the inlet or exit area, respectively. In these areas, the respective fluid flow splits or accumulates.
An “exposed cross section” is produced where the inlet area overlaps with the exit area.
Due to the large pressure differential between the two fluids, the individual plies must be capable of withstanding the highly disparate pressure levels in the region of the exposed cross section.
The large surface area acted upon by pressure in the region of the exposed cross section causes high material tensions to occur. This can result in material deformations, e.g., flowing or failure of the component.